Wireless sensing systems may be applied outdoors or indoors. The outdoor applications include the forest ecology monitoring and the like. The indoor applications include, for example, the detection of the concentration of carbon dioxide in the factory, the indoor temperature monitoring, and the like. A wireless sensor in the wireless sensing system senses, collects and sends back the data.
At present, the user may perform the data aggregation query on the wireless sensing system, for example, the sum, average, counting, histogram and maximum of the sensed data. The common applications of the data aggregation query include, for example, querying the average gas consumption in a certain zone, querying the number of the active sensor nodes in the wireless sensing system or the maximum rainfall in a zone.
At present, the well-known data aggregation method in the wireless sensor system is the tree-based data aggregation computation. A spanning tree is constructed with respect to the wireless sensing system, wherein one of the wireless sensors (i.e. nodes) serves as a root node, and other wireless sensors serve as internal nodes. For example, in the computation of sum aggregation, the bottommost layer of sensor nodes sends (or broadcasts) their sensed readings to the upper layer of sensor nodes. Each sensor node sums the sensed readings transferred from all the child nodes and its own sensed readings to calculate the new partial aggregated value, which is then sent to the parent node. Thus, the operation is performed level by level (or node by node), and a final aggregate is finally calculated at the root node.
In addition, in order to enhance the reliability and the fault-tolerance ability, the multi-path data aggregation computation is applied to the sensing data aggregation computation of the wireless sensing system. In the multi-path data aggregation computation, a directed acyclic graph is used to connect each sensor node of the wireless sensing system. In the multi-path data aggregation computation, the sensor node broadcasts its own sensed reading to all nodes on the upper layer. Because one sensed reading is copied into multiple copies and transferred and calculated in the network, the sensed reading of the sensor node cannot be lost until all the copies are lost. So, its reliability is better. In the multi-path data aggregation computation, however, the same data may be calculated repeatedly so that the double counting problem is induced and the result of data aggregation query may be incorrect.
Thus, the example embodiment of the present disclosure discloses a wireless sensing system and a method thereof, capable of performing the multi-path based data aggregation computation based on the dynamic counting.